This invention relates to a method of reduction of compounds forming on a substrate at least one surface layer such as, for example, the oxide layer which is capable of forming spontaneously at the surface of a substrate and is applicable in particular to the fabrication of field-effect semiconducting structures of the type designated as MIS (metal-insulator-semiconductor).
It is known that a cleaved metal or semiconductor surface subjected to chemical, ionic or thermal attack is covered with a thin film of oxide and possibly of other adsorbed chemical species in a very short time of the order of a few seconds after treatment. The thickness of the film-layer thus formed is smaller than one hundred Angstroms.
This phenomenon is not without drawbacks in the techniques adopted in microelectronics or submicroelectronics and more generally in all techniques involving the formation of thin films. The result is in fact seen in deep modifications of physico-chemical, optical and/or electronic properties of the surface of such films.
One particularly significant example illustrating the extent of this phenomenon is provided by recent techniques in which gallium arsenide substrates are employed for the development of high-performance integrated circuits, especially those comprising MOS, MIS or other similar types of elements. These devices make it necessary to form dielectric, semiconductor and/or metal layers. In this type of integrated circuit, there exists a relationship between the ratio of oxygen coverage of the substrate surface and the surface curvature of the associated band diagram, which consequently establishes the Fermi level in the surface regions approximately at the center of the forbidden band. The properties of the material are therefore not wholly retained up to the surface, thereby adversely affecting the operation of most devices which are formed on these substrates.
In order to overcome the disadvantages recalled in the foregoing, one solution would consist in cleaning the surface of the substrate and in performing all the successive operations of fabrication of these devices within a vessel in which is maintained a very low pressure commonly known as "ultra-high" vacuum (a pressure of less than 10.sup.-11 Pa approximately).
In addition to the very high costs and the complexity of application associated with this type of technique which preclude its use as an operational industrial process, there in any case exists a potential danger of subsequent contamination of the surface at the time of return to normal atmospheric conditions.